This proposal addresses the general problem of the regulation of enzyme development during metabolic adaptations or differentiation. Its major focus is the mechanism and regulation of selective inactivation and degradation of enzymes. A secondary focus is on the regulation of synthesis of those enzymes which are also the targets of selective degradation processes. The experimental system chosen is the bacillus subtilis, in which we have identified and characterized two instances of rapid degradation in nutrient-starved (sporulating) cells. The targets of these processes are key enzymes of nucleotide biosynthesis: aspartate transcarbamylase (ATCase) and glutamine PRPP amidotransferase. The former is inactivated and degraded in an energy-dependent manner. Degradation of amidotranferase appears to be preceded by oxidative inactivation of an essential (4Fe-4S) prosthetic group. We have also shown that the synthesis of these two enzymes is rapidly and selectively terminated prior to degradation. Many proteins--but not the two discussed above-are targets for degradation by another proteolytic system that develops during sporulation. Ornithine transcarbamylase is degraded by this latter system. Research into the nature of these specific degradation processes using immunochemical methods and attempted biochemical reconstruction from purified components is proposed. The relationships of these processes to bulk protein turnover will be examined. The possible regulation of ATCase synthesis by alterations in RNA polymerase will be examined using cloned DNA coding for ATCase.